The present invention relates to an apparatus and a method for reading a coded pattern, symbol or indict. More particularly, the present invention relates to a barcode reader and method for improving captured resolution with a fiducial input closed loop system.
In situations where coded patterns, symbols or indict such as a barcode are being read, such as by using a handheld barcode reader or scanner, there is a certain degree of xe2x80x9coverheadxe2x80x9d built into reading systems of the barcode reader. This is done in order to accommodate misalignment and improper sizing of the barcode within the image sensor area of the barcode reader. This xe2x80x9coverheadxe2x80x9d is in the form of unused pixels of the image sensor area around the pixels which record the barcode itself. In many instances this overhead is not troublesome because the barcode is of significantly lesser resolution than the sensor, meaning that even when ineffectively oriented in relation to the barcode, the barcode reader still has the resolution required to capture the entire barcode image.
This xe2x80x9coverheadxe2x80x9d can become a problem when the resolution of the sensor is not significantly greater than that required to image the barcode. This is the case when a low-resolution sensor is selected for an application for cost reasons. Also, this is the case while imaging two dimensional barcode formats which encode large amounts of data with a hand held reader. Storing sound files as invisible encodements and capturing them with a hand held reader is an example of a system that would benefit from this invention (see, for example, co-pending applications U.S. Ser. No. 09/122,502 and U.S. Ser. No. 08/931,525, as well as U.S. Pat. No. 5,313,235.
Due to the cost of two dimensional CCD and CMOS sensors increasing with increased resolution, for any application it is desirable to maximize the number of pixels which are used to capture meaningful barcode data.
U.S. Pat. No. 5,378,883 discloses a barcode reader with variable optics capable of reading over large distance ranges. The focal length of the lens however is determined by a distance measurement to the target, and therefore is not ideally suited to imaging barcodes of significantly different sizes.
U.S. Pat. No. 5,710,417 provides the ability to alter the aspect ratio, image resolution, and size of a captured image in a bar code reader, however these changes to the scanner must be programmed into the unit and therefore are not closed loop based on a pre-scanned image analysis.
Marker beams and other aiming aids such as framing devices (U.S. Pat. No. 5,793,033) are often used to try to minimize the problem solved by this invention. Any of these methods still rely exclusively on the proper operation and skill of the operator to achieve the desired result.
Conventional arrangements as well as the above-mentioned patents do not disclose or suggest a closed loop system for correcting improper focal length, skew or aiming based on a pre-scan of an image to locate image fiducials.
An object of the present invention is to provide for a barcode reader and method which improves the resolution of captured barcode images.
The present invention relates to a method for reading a coded pattern. The method comprises the steps of performing a pre-scan on the pattern by using a reader having imaging optics; identifying a marker arrangement on the pattern; determining a minimum field of view that will substantially capture the marker arrangement; actuating a variable magnification imaging system to the minimum field of view; and capturing a full resolution final image of the pattern.
The present invention also relates to an apparatus for reading a coded pattern. The apparatus comprises an illumination source for illuminating a pattern within a field of view; a sensor onto which the pattern is imaged; imaging optics which image the pattern onto the sensor at a first magnification; and a processing unit adapted to receive a signal from the sensor indicative of the imaged pattern, perform a pre-scan of the imaged pattern, and locate a marker arrangement on the pre-scanned pattern. The processing unit controls the imaging optics to set a second magnification and to perform a final scan on the imaged pattern at the second magnification.
In one example of an embodiment of the present invention, a barcode reader for capturing barcode files uses a zoom lens which, based on feedback from a prior scan of the barcode is capable of changing the focal length to optimize the scan of the barcode. An implementation of this invention has the marker arrangement in the form of two distinct markers in opposing corners of the printed barcode. After sensing their position in the pre-scanned frame, the reader zooms to an optimal position for maximizing the resolution of the sensor. A further feature of the invention incorporates the above embodiment, and also includes additional corrections to compensate for skew and aim using the same methodology.
The barcode reader and method of the example of the present invention described above improves the resolution of captured barcode images by limiting the number of unused pixels on the sensor of the barcode reader by: performing a pre-scan of the barcode image, identifying sensor pixel locations containing coner fiducials of the barcode, performing calculations from these sensor locations to determine the maximum lens focal length that will still capture these coner fiducials, actuating a zoom lens on the barcode reader to this focal length, and capturing a full resolution final image.